In the field the species survives for a year or less. Survival rates are very low. Only 2-5 percent of the population will reach maturity. An estimate of the number of eggs per female per season is 53,500. Each spawn mass contains 1,000 - 1,500 eggs. The egg mass has a definite ring doughnut shape and the colour of the mass varies with diet. Individual egg size is around 100 microns. Development inside the egg takes 2.5 to 3.5 weeks. Spawning occurs throughout the year but there is a distinct peak. In southern Britain this peak is in winter resulting in main larval settlement in late May / early June. Further north settlement peaks in September. Cold temperatures may delay oviposition. Settlement is probably induced by organic properties of substrata beneficial to the adult rather than the presence of or exudate from other individuals of the species.